Black carbon aerosols (BC), as products of incomplete combustion activities (e.g., diesel engines, residential solid fuel, open burning), have attracted widespread interest because they not only have an impact on climate and the environment but also have a negative impact on human health (Cassee et al., 2013; Peng et al., 2016). BC emissions in East Asia are among the highest in the world (Bond et al., 2013), and Beijing, as a mega-city in East Asia, is not to be underestimated in terms of BC emissions from transportation, industry, and residential use (Zhang et al., 2013). In addition, the aging process of BC is complicated by the complex air pollution caused by the rapid urbanization and the increase in vehicles in Beijing (Liu et al., 2019a, 2020a). Much research in recent years has focused on the mixing state of BC, such as coating thickness and aerosol components mixed with BC (Liu et al., 2019a; Xie et al., 2020). However, few researchers have addressed the problem of the relationship between morphology, coating thickness, and coating composition. The morphology of BC has a great influence on the assessment of its absorption properties and radiative forcing (Wang et al., 2021). It is worth noting that during major events, air quality tends to be better in Beijing and surrounding areas due to the strict control measures (Guo et al., 2013; Sun et al., 2016). The detailed characterization of the mixing state of BC in different environments is essential for understanding the aging of BC in the atmosphere.
Studies based on laboratory and field observations have shown significant differences in particle size from different types of aerosols and different emission sources (Fennelly, 2020; Fröhlich-Nowoisky et al., 2016; Li et al., 2016); for example, coarse particulate emissions from coal combustion are generally higher than those from biomass (Yang et al., 2021). There are also differences in the harmful systemic health effects of particles at different aerodynamic diameters (Dae) (Kwon et al., 2020); for example, ultrafine particles (PM1.0) retained longer in the lung than fine particles (PM2.5) (Schraufnagel, 2020). It has been shown that the morphology, optical properties, coating thickness, hygroscopicity and coating composition of BC-containing particles with different particle sizes are very different (Liu et al., 2020b; Wu et al., 2019a; Xie et al., 2020). Therefore, the characterization of size-resolved BC is crucial for understanding the health effects of BC, improving the assessment of its absorption-enhancing effects, and quantifying its impact on climate.
There are two main types of technical methods used to study size-resolved BC morphology and mixing state. One of the methods is to directly observe the morphology of a single BC using electron microscopy or atomic force microscopy (Li et al., 2016), but it cannot meet the demand of real-time, continuous, and high-frequency online analysis. Another technique is to use a single-particle soot photometer (SP2) in tandem with other particle size screening instruments (DeCarlo et al., 2004; Liu et al., 2019b, 2020b), which can overcome the shortcomings of the former. Many researchers have used a differential mobility analyzer (DMA) and SP2 to characterize BC morphology and mixing state (Han et al., 2019; Hu et al., 2021; Wu et al., 2019b; Zhang et al., 2018a). However, the method is limited by the way the DMA selects the particle diameter, i.e., the electrical mobility related to both the mobility and aerosol charges, which can allow unwanted mobility diameter aerosols to be screened out (Wang and Flagan, 1990; Wu et al., 2019b). Recently, an aerodynamic aerosol classifier (AAC) has been introduced to replace the DMA in tandem systems (Liu et al., 2020b; Yu et al., 2022), selecting aerosols with a certain aerodynamic diameter and thus avoiding the effect of aerosol charge. This is of great significance for understanding both the BC morphology and the mixing state in the real atmosphere and quantifying the direct or indirect climate effect of aerosols.
BC, i.e., freshly emitted BC mixed with other compounds in the atmosphere through the aging process to become coated BC. During aging, the morphology, coating thickness, coating composition, and absorption ability will change. Generally, the more aged BC is, the thicker the coatings, the higher the hygroscopicity, the more regular the morphology, and the stronger the absorption enhancement (He et al., 2015; Peng et al., 2016). Based on the developed instruments, it is now established from a variety of studies that particle morphology is commonly described by the dynamic shape factor (DeCarlo et al., 2004). Liu et al. (2020b) found that the dynamic shape factor of refractory black carbon-containing particles (rBC) decreased from 1.43 to 1 and that the coating thickness of rBC increased from 1.67 to 2.84 as Dae increased from 200 to 700nm. This means that as the Dae of rBC increases, rBC becomes progressively more regular in morphology and tends to be spherical. The effective density of rBC increased as the dynamic shape factor decreased (Liu et al., 2019b). Wu et al. (2019a) found that an increased inorganic fraction and more oxidized organic coatings usually determine a thicker coating thickness and larger rBC size. Overall, there are relatively few studies on the microphysical properties of size-resolved rBC, particularly in relation to the morphology, mixed material, and coating thickness of size-resolved rBC.
A previous study (Liu et al., 2020b) characterized the coating thickness, optical properties, and morphology of size-resolved rBC in Beijing using an AAC-SP2 tandem method. To explore the size-resolved coating material, we performed a novel online measurement system by coupling an aerodynamic aerosol classifier (AAC) with different aerosol measurement instruments, including a single-particle soot photometer (SP2) and a single-particle-aerosol mass spectrometer (SPA-MS). Several studies have been carried out to characterize the coating composition of BCc using SPA-MS (Sun et al., 2022; Xie et al., 2020). It is worth noting that this measurement was conducted at an urban site during the XXIV Olympic Winter Games with relatively clean air conditions in Beijing. Measurement of the size-resolved mixing state of rBC illustrates the difference between irregular and regular rBC. In addition, we conducted a detailed analysis of the mixing state, absorption ability and morphology of rBC at special time points during the Winter Olympics and under the influence of different source air masses. These results enhance the understanding of the climate and environmental effects of different rBC types under different pollution conditions and provide morphology-composition-coating thickness relationships that can be used to constrain climate and air quality modeling.
The measurement of rBC was performed from 10 February to 1 March 2022at the State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry (LAPC, latitude: 39.97°N, longitude: 116.37°E). The sampling site is located between the North 3rd and 4th Ring Road of Beijing and is adjacent to the Jingzang highway. It is less than 2km away from Beijing's Bird's Nest Stadium, the venue for the opening ceremony of the XXIV Olympic Winter Games (Fig. 1b). Transportation emissions
Overview of the field observations
Fig. 2 and Fig. S6 show the time series of meteorological parameters and pollutants measured at the LAPC site during the campaign. The average mass concentration of PM2.5 during the observation period was 28μgm−3, which is 48μgm−3 lower than the average concentration from 2014 to 2022 and is the lowest concentration in the last 8 years (Fig. 1e). This may be related to the control measures implemented in Beijing between January and March 2022. As illustrated in Fig. 2, according to
Conclusions and implications
A novel tandem system consisting of an AAC, a SP2, and a SPA-MS was conducted to explore the aerodynamic size-resolved coating thickness, light absorption properties, and coating components coated on the rBC core of rBC-containing particles in Beijing during the XXIV Olympic Games. Two aerodynamic size (Dae=200nm and Dae=300nm) rBC particles were selected during the whole observation to study the effect of relative differences in morphology on the coating thickness, coating compositions,
CRediT authorship contribution statement
Yuting Zhang: Conceptualization, Experiment, Methodology, Software. Hang Liu: Investigation, Experiment. Shandong Lei: Investigation. Aodong Du: Investigation, Software. Weijie Yao: Investigation. Yu Tian: Investigation. Yele Sun: Investigation. Jinyuan Xin: Investigation. Jie Li: Investigation. Junji Cao: Resources. Zifa Wang: Resources, Supervision. Xiaole Pan: Conceptualization.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
This study was supported by the National Key Research and Development Program of China (No. 2022YFC3701000, Task 4).
Identifying the airport as a key urban VOC source in the Pearl River Delta, China
Atmospheric Environment, Volume 301, 2023, Article 119721
Volatile organic compounds (VOCs) are the main precursors of ozone (O3) and secondary organic aerosol (SOA) formation in the atmosphere. The traditional positive matrix factorization (PMF) source apportionment method is mainly based on the time series of VOCs at a single site, and its results cannot indicate the difference spatially. In this study, a refined spatial distribution study was carried out in Shenzhen in the Pearl River Delta (PRD) region, China, with 110 sampling sites covering the city. Ninety-two VOC compounds were quantitatively analyzed and the spatial distribution characteristics of various VOCs were obtained. Based on the PMF source apportionment of multisite samples, five types of sources and their spatial distributions of vehicle exhaust, gasoline leakage, industrial processes, airport-related sources and regional transport were identified. The airport source was resolved for the first time in the VOC source apportionment and was further verified by the measured source spectra in the airport. It is found that the airport-related sources accounted for 19% of the ambient VOC concentrations in Shenzhen and had strong Cl radical reaction activity, indicating that the airport-related sources may have a greater impact on O3 and SOA formation in coastal cities than previously expected.
Water-soluble brown carbon in atmospheric aerosols from the resource-dependent cities: Optical properties, chemical compositions and sources
Journal of Environmental Sciences, 2023
As a vital type of light-absorbing aerosol, brown carbon (BrC) presents inherent associations with atmospheric photochemistry and climate change. However, the understanding of the chemical and optical properties of BrC is limited, especially in some resource-dependent cities with long heating periods in northwest China. This study showed that the annual average abundances of Water-soluble BrC (WS-BrC) were 9.33±7.42 and 8.69±6.29 µg/m3 in Baotou and Wuhai and the concentrations, absorption coefficient (Abs365), and mass absorption efficiency (MAE365) of WS-BrC presented significant seasonal patterns, with high values in the heating season and low values in the non-heating season; while showing opposite seasonal trends for the Absorption Ångström exponent (AAE300-400). Comparatively, the levels of WS-BrC in developing regions (such as cities in Asia) were higher than those in developed regions (such as cities in Europe and Australia), indicating the significant differences in energy consumption in these regions. By combining fluorescence excitation-emission matrix (EEM) spectra with the parallel factor (PARAFAC) model, humic-like (C1 and C2) and protein-like (C3) substances were identified, and accounted for 61.40%±4.66% and 38.6%±3.78% at Baotou, and 60.33%±6.29% and 39.67%±4.17% at Wuhai, respectively. The results of source apportionment suggested that the potential source regions of WS-BrC varied in heating vs. non-heating seasons and that the properties of WS-BrC significantly depended on primary emissions (e.g., combustion emissions) and secondary formation.See AlsoMétodos de Fluorescencia para la Detección de Bioaerosoles en sus Aplicaciones Civiles y Militares.Mediciones finas de PM: monitoreo del aire personal e interiorConcentración ambiental de esporas de hongos en una metrópolis subtropical: distribuciones temporales y determinantes meteorológicosManual de Bioaerosoles
In-situ measurement of secondary aerosol formation potential using a flow reactor: Livestock agricultural area
Atmospheric Environment, Volume 301, 2023, Article 119695
Atmospheric ammonia (NH3) is an important particulate matter (PM) precursor. The primary sources of ammonia in agriculture are livestock farming and synthetic fertilizers. Here, an oxidation flow reactor (OFR) was deployed in the vicinity of livestock farming during the summer of 2020 and winter of 2021 to determine the extent of secondary aerosol formation. The OFR was run in a 1-h cycle of different aging times for the daytime and nighttime oxidants of OH and NO3 radicals, respectively. The daytime reaction periods were 05:00–20:00 and 08:00–18:00, respectively, for summer and winter. Ambient and aged PM2.5 were characterized for secondary aerosol formation potential (AFP) using a time-of-flight aerosol chemical speciation monitor (ToF-ACSM). Ambient PM2.5 mean composition during summer was dominated in the order of nitrate (41%), organic matter (33%), ammonium (15%), and sulfate (11%). Secondary AFP was in the higher order, nitrate (71%), ammonium (20%), organic matter (8%), and sulfate (1%). A prominent effect of NH3 was observed when the primary aerosol was aged at high NOx and relative humidity (RH). Source apportionment revealed secondary organic aerosol (SOA)-dominant organic aerosols.
Enhanced ozone pollution in the summer of 2022 in China: The roles of meteorology and emission variations
Atmospheric Environment, Volume 301, 2023, Article 119701
The variation of surface ozone (O3) is linked to changes in meteorology and emission. A record-breaking high temperature struck China in the summer of 2022, resulting in positive anomalies of daily maximum temperature of 0.86±1.02°C. Consequently, the mean daily maximum 8h average (MDA8) ozone (O3) increased by 6.46±13.0μgm−3 compared to the mean summertime MDA8 O3 from 2014 to 2021 in China. This research aimed to understand the impact of meteorology and emission changes on O3 variations in different regions in the summer of 2022 by an explainable machine learning method. Results showed that the changes in emissions dominated the O3 enhancement in the Pearl River Delta (PRD), Beijing-Tianjin-Hebei (BTH), and Twain-Hu Basin (THB) with contributions of 89%, 86%, and 53% respectively. Satellite observations suggested that the increased O3 due to emission changes in BTH and PRD were related to the decreases in NO2 emissions and increases in volatile organic compound (VOC) emissions. On the contrary, variations in meteorology contributed 63%, 63%, and 51% respectively to the increases of O3 in the Sichuan Basin (SCB), Yangtze River Delta (YRD), and Fen-Wei Plain (FWP). The increase in O3 levels due to meteorological changes was associated with an anomalous westward extension of the Western Pacific Subtropical High during the summer of 2022. Specifically, the decrease in relative humidity, increases in temperature and boundary layer height were the dominant factors contributing to the increase of meteorology related O3 in SCB, THB, and YRD, with contributions over 99%. This study recommends a continuous reduction in O3 precursor emissions to mitigate O3 pollution under the global warming background.
Secondary aerosol formation drives atmospheric particulate matter pollution over megacities (Beijing and Seoul) in East Asia
Atmospheric Environment, Volume 301, 2023, Article 119702
Atmospheric particulate matter (PM) pollution in Beijing and Seoul is an urgent concern because of the dense population and the role of the capital city. This study aimed to understand haze formation over East Asia during winter by simultaneously measuring the in situ aerosol chemical composition in the two megacities. During the sampling period, a similar pollution situation characterized by extremely low SO2 (approximately 1ppbv) and high NOx (approximately 20ppbv) concentrations and secondary inorganic aerosol (SIA)-dominated PM was found in both cities. Nitrate dominated the inorganic components in the submicron particles in both cities and was more pronounced in Seoul than in Beijing. The enhanced SIA mass concentrations during pollution episodes were observed to be associated with an increased local atmospheric oxidation capacity (indicated by O3+NO2=Ox concentration) and ambient relative humidity under similar stagnant weather conditions. Regarding the thermodynamic equilibrium, abundant aerosol liquid water promoted the partitioning of gaseous HNO3 into its particle phase when pollution events occurred. This result emphasized the importance of local secondary aerosol formation for atmospheric PM pollution in East Asian megacities. The box model simulation of nitrate formation indicated that the homogeneous oxidation of NO2 by OH radicals was the major nitrate formation pathway in both megacities. The downward transport of nitrate from the residual layer also significantly contributed to nitrate concentrations. NOx and volatile organic compounds (VOCs) exhibited a non-linear relationship with nitrate formation. Reducing VOCs concentrations was an efficient approach to mitigate nitrate in both megacities. A reduction of more than 50% in NOx concentrations was required for the effective reduction of nitrate. This study highlighted that Beijing and Seoul were experiencing similar PM pollution situations, and nitrate reduction should be considered to improve their air quality.
Source apportionment of potentially toxic PM10 near a vast metallic ore mine and health risk assessment for residents exposed
Atmospheric Environment, Volume 301, 2023, Article 119696
Mining is an economic activity that traditionally releases large amounts of particulate matter into the atmosphere because of the procedures required to process the mineral. In particular, polymetallic ores are environmentally harmful as they can enrich potentially toxic elements, which may cause adverse effects to humans and ecosystems due to their toxicity. The aim was to assess the impact on health of this type of mining on nearby populations. Accordingly, it was conducted an extensive PM10 sampling campaign during the entirety of 2021 through a total of 248 filters placed in three villages close to the Rio Tinto district (Southwest Spain), which is one of the largest Cu mines in the world. A total of 58 major and trace elements were analysed, along with organic carbon/elemental carbon, cations, and anions. The mean PM10 concentrations were high during spring (47 μgPM10⋅m−3) and summer (56 μgPM10⋅m−3) in the population closest to the mine, wherein values surpassed the annual and daily limit values, but were lower in the other two villages. Moreover, high enrichment of As (annual maximum mean of 6.2ng⋅m−3), Cu (70ng⋅m−3), Pb (19ng⋅m−3), and Zn (50ng⋅m−3) was observed in all locations. A positive matrix factorization (PMF) was primarily used to assess the origins of this particulate matter, revealing that the impact of the mine reduced considerably over a long distance, with contributions ranging from 36% at the mine's outskirts to 8% further away from it, which coincides with the features of the mine during the abandonment phase (2001–2015). Despite this, the risk assessment revealed that the carcinogens were within the permissible exposure limits even in the closest village, indicating a minor concern for the inhabitants from a toxicological perspective.
© 2023 Published by Elsevier Ltd.